The present invention relates to a process for the production of a cellular composite, and to the cellular composites produced by this process. This process comprises preparing a mixture of inorganic hollow microspheres, water and a polyisocyanate, filling a mold completely with this mixture, and heating the mold to a temperature of from 100 to 280° C. This causes the polyisocyanate to react with the water and form a polyurea which binds the hollow microspheres, thereby forming a cellular composite.
Polyisocyanates are known to be suitable binders for solid particles of various compositions, e.g. wood flakes, sand, sawdust, etc. They are also known to be used in the production of foams and syntactic foams as a co-reactant for polyurethanes. The use of polyisocyanates as a binder for hollow particles, e.g. hollow microspheres, has not, however, been previously known and/or expected.
U.S. Pat. Nos. 4,785,024, 4,843,104, 5,271,886, 5,278,194, 6,235,800 and 6,235,810 disclose various polymeric microspheres and syntactic foams. However, none of these disclose that a composite can be formed from microspheres and a binder component. U.S. Pat. Nos. 4,850,849, 4,913,872, 5,433,905 and 5,674,568 describe various binders that are suitable to prepare wood composites from wood and wood furnish. These patents do not disclose inorganic microspheres.
Surprisingly, it has now been found that the proper selection of polyisocyanate functionality and viscosity, combined with the use of water as a co-reactant, forms a suitable binder for hollow microspheres that results in the formation of a cellular composite having a high compressive strength and low density at typical (conventional) binder concentrations.
Composites of this type could be used commercially as a low weight core for furniture laminates, or as a building panel in residential or commercial construction. With the addition of optional combustion modifiers, this mostly inorganic composite would offer excellent fire performance in special institutional and aerospace applications. The composition of the hollow microsphere's shell would be chosen, for example, based on the desired fracture strength of the shell and cost.